1. Field of the Invention
This invention relates to a dry particulate thickener for liquids and to a process for making it. The thickener consists of organic fibrid particles having a very small size, a very high aspect ratio, and a very low bulk density. The process for making the thickener includes steps of drying coagulated fibrids in a way that results in a product with very high surface area.
2. Description of the Prior Art
U.S. Pat. No. 2,988,782, issued Jun. 20, 1961 on the application of Parrish et al., discloses the preparation and use of fibrids made from several synthetic polymers. While it is disclosed that the fibrids can be dried before use, the fibrids are made without regard to aspect ratio and are used almost exclusively in paper products. There is no mention of fibrids as thickening agents.
U.S. Pat. No. 2,999,788, issued Sep. 12, 1961, on the application of Morgan, discloses the preparation of synthetic polymer fibrids. There is no mention of using fibrids for liquid thickening purposes and there is little mention of using dried fibrids.
U.S. Pat. No. 4,519,873, issued May 28, 1985 on the application of Amano et al., discloses preparation of pulp-like aramid particles used to make papers for electrical insulation. The particles are made in an aqueous system and are used without drying. It is taught that the particles must have a freeness of less than 80 milliliters to be useful.
Japanese Patent Publication (Kokai) No. 36167/82, published Feb. 26, 1982, discloses the preparation of fibrids of, for example, aromatic polyamides, by means of shearing a precipitating liquid system of the polyamide. The fibrids are isolated from the liquid and are dried; and, then, they are ground into small particles. The publication states that previous attempts at making particles which would be effective thixotropic agents failed because the particles were too large and the wrong shape.